Living communities in rivers and streams

Abstract

Abstract Living communities in streams and rivers are diverse and spatially variable. Are differences driven by environmental factors or by species interactions? Communities are assembled from species locally available with traits that enable them to survive. Dispersal ability can also limit presence. At large scales, most groups of organisms (with interesting exceptions) are most diverse at low latitudes. At smaller scales, there are strong patterns along rivers, and laterally and vertically away from the channel. Communities change with time, so can we distinguish ‘natural’ fluctuations from sustained change? Sustained changes are often associated with anthropogenic impacts (e.g. on water quality, or due to climatic shifts). How important is ‘disturbance’ (discrete events, such as floods and droughts) for communities—and how far is it mitigated by refugia? The physical nature of river systems as branching networks with divided local communities in different ‘patches’ could promote overall stability via dispersal among them.